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A semi-truck travels on a paved road for 2 hours at an average speed of 20 miles per hour faster than it travels on a dirt road. The time spent on the dirt road is 3 hours. If the entire trip is 200 miles, how fast is the truck traveling on the dirt road?

  • Math -

    Use d = r * t for both the paved and the dirt roads. Use x for the unknown speed on the dirt road.

    For the paved road, use d1 (distance 1):
    d1 = r * t
    d1 = (x + 20) * 3
    d1 = 3(x + 20)

    For the dirt road, use d2 (distance 2):
    d2 = r * t
    d2 = x * 3
    d2 = 3x

    Also, you know that the distance traveled on the paved road, d1, and the distance traveled on the dirt road, d2, sum to 200 miles. Thus, you know:
    d1 + d2 = 200

    See if you can take it from there.

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